Here's an exercise that my old bass teacher taught me. Do this for 4-5 minutes/day as part of your warm-up routine:
1. Find a spot on your bass neck where you can play 4 fingers per note across 4 consecutive frets comfortably.
2. Set your metronome around 50-60 bpm.
3. Play whole-notes moving up and down from 1st finger to pinky and back. Focus on keeping your fingers close to the string (when you raise them) and on the string (when behind the note you're fretting). Also focus on maintaining good time and a clean left- and right-hand attack.
4. Once you're comfortable with whole-notes, move to half-notes, again playing 1 note per fret. Then quarters, then 8ths, then triplets, then 16ths, then 16th-note triplets. Then start moving the metronome click up (or down if it's too fast).
5. Then, start incorporating shifts - play the exercise going up from first finger to pinky, but then instead of descending, shift from pinky to first finger on the next fret up and continue. Focus on a smooth shift. Do the same descending - shift from first to pinky. Repeat for all the sub-divisions.